Colorectal cancer (CRC) is a leading cause of cancer death in the United States. Screening for CRC reduces CRC mortality, yet rates of screening in the United States remain low. Fecal occult blood testing (FOBT) is the only CRC screening method with an established positive balance of benefit and risk, is the least expensive, and is the preferred method for nearly half of patients. A newer fecal screening test, the fecal immunochemical test (FIT), offers significant improvements over the FOBT. It is easier to use and is more sensitive at detecting both CRC and precancerous adenomas than the FOBT. The OC-Micro FIT is of particular interest because it is highly sensitive and specific and it is the only FIT test approved in the US that can be processed in an automated manner. Thus, the OC-Micro is an optimal method for use in mass screening programs to improve community CRC-screening rates. However, prior studies of OC-Micro suffer from several limitations: they were conducted in populations not optimal for assessing screening performance in average risk patients in the U.S. and the studies did not clearly establish optimal number of samples required and cut-points for test positivity. Therefore, the overall goal of the MY-FIT (Maximizing the Yield of Fecal Immunochemical Tests) study is to capitalize on the highly integrated and extensive electronic medical record system of the study site to collect two separate sets of data that, when synthesized, will provide a thorough picture of the comparative patient adherence to, sensitivity, specificity, and costs of different protocols for using the OC-Micro FIT. Specifically, among KPNW members aged 50-75 who are at average risk for colorectal cancer (CRC) and who are due for CRC screening (n=78,000), we propose to: 1. Compare the sensitivity, specificity, positive predictive value, and negative predictive value for colorectal cancer and advanced adenoma (advanced neoplasia) between a single-sample FIT (1-FIT) and a two- sample FIT (2-FIT) using varying cut points for a positive test (n=2100). 2. Compare patient adherence to completion of a 1-FIT versus a 2-FIT protocol (n=3000). 3. Assess and compare cost per screen for a 1-FIT versus a 2-FIT protocol, and the cost per advanced neoplasia detected in a 1-FIT versus a 2-FIT protocol (using varying cut points for a positive test) (n=78,000). Answering the above questions will provide a much-needed strong evidence base for a best-practice, cost- effective method of using the OC-Micro FIT to screen for CRC in a general U.S. population. PUBLIC HEALTH RELEVANCE: Colorectal cancer (CRC) is the second leading cause of cancer death in the United States, and affects men and women almost equally. Screening for CRC reduces deaths from this cancer, yet rates of screening in the United States remain low. This project aims to provide evidence to guide use of a newer screening test, the fecal immunochemical test (FIT), to replace the most widely used fecal test, the FOBT. FITs are easier to use, more accurate, and cheaper than current methods of fecal testing, and are ideal for use in the general population. However, these tests have not been tried in large populations. Our project will answer questions about the best, most accurate way to use this improved test for colon cancer.